x86: Use __builtin_object_size() to validate the buffer size for copy_from_user()

gcc (4.x) supports the __builtin_object_size() builtin, which
reports the size of an object that a pointer point to, when known
at compile time. If the buffer size is not known at compile time, a
constant -1 is returned.

This patch uses this feature to add a sanity check to
copy_from_user(); if the target buffer is known to be smaller than
the copy size, the copy is aborted and a WARNing is emitted in
memory debug mode.

These extra checks compile away when the object size is not known,
or if both the buffer size and the copy length are constants.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
LKML-Reference: <20090926143301.2c396b94@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 4 insertions, 4 deletions

diff --git a/arch/x86/lib/copy_user_64.S b/arch/x86/lib/copy_user_64.S
index 6ba0f7bb85ea..4be3c415b3e9 100644
--- a/arch/x86/lib/copy_user_64.S
+++ b/arch/x86/lib/copy_user_64.S
@@ -78,7 +78,7 @@ ENTRY(copy_to_user)
 ENDPROC(copy_to_user)
 
 /* Standard copy_from_user with segment limit checking */
-ENTRY(copy_from_user)
+ENTRY(_copy_from_user)
         CFI_STARTPROC
         GET_THREAD_INFO(%rax)
         movq %rsi,%rcx
@@ -88,7 +88,7 @@ ENTRY(copy_from_user)
         jae bad_from_user
         ALTERNATIVE_JUMP X86_FEATURE_REP_GOOD,copy_user_generic_unrolled,copy_user_generic_string
         CFI_ENDPROC
-ENDPROC(copy_from_user)
+ENDPROC(_copy_from_user)
 
 ENTRY(copy_user_generic)
         CFI_STARTPROC
diff --git a/arch/x86/lib/usercopy_32.c b/arch/x86/lib/usercopy_32.c
index 1f118d462acc..8498684e45b0 100644
--- a/arch/x86/lib/usercopy_32.c
+++ b/arch/x86/lib/usercopy_32.c
@@ -874,7 +874,7 @@ EXPORT_SYMBOL(copy_to_user);
  * data to the requested size using zero bytes.
  */
 unsigned long
-copy_from_user(void *to, const void __user *from, unsigned long n)
+_copy_from_user(void *to, const void __user *from, unsigned long n)
 {
         if (access_ok(VERIFY_READ, from, n))
                 n = __copy_from_user(to, from, n);
@@ -882,4 +882,4 @@ copy_from_user(void *to, const void __user *from, unsigned long n)
                 memset(to, 0, n);
         return n;
 }
-EXPORT_SYMBOL(copy_from_user);
+EXPORT_SYMBOL(_copy_from_user);